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Undulator Spectra as a Diagnostic for Electron Beam Energy Spread and Emittance

Undulator Spectra as a Diagnostic for Electron Beam Energy Spread and Emittance. M. Bakeman, J. van Tilborg, T. Sokollik, C. Toth, W. Fawley, C. Schroeder, K. E. Robinson, E. Esarey, and W. Leemans Lawrence Berkeley National Laboratory. Introduction. Loasis 1GeV Laser Wakefield Accelerator

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Undulator Spectra as a Diagnostic for Electron Beam Energy Spread and Emittance

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  1. Undulator Spectra as a Diagnostic for Electron Beam Energy Spread and Emittance M. Bakeman, J. van Tilborg, T. Sokollik, C. Toth, W. Fawley, C. Schroeder, K. E. Robinson, E. Esarey, and W. Leemans Lawrence Berkeley National Laboratory

  2. Introduction • Loasis 1GeV Laser Wakefield Accelerator • Undulator Radiation as a beam diagnostic • THUNDER Undulator Characterization • Quadrupole Electron Beam Transport • XUV Spectrometer Design and Calibration • Conclusions and Future Work

  3. First GeV Electron Beam from LWFA Laser: a0 ~ 1.46 (40 TW, 37 fs) Capillary: D = 312 mm; L = 33 mm expt. sim.* 1 GeV beam 3 W.P. Leemans et. al, Nature Physics 2 (2006) 696; *Simulation using VORPAL

  4. Undulator Radiation Diagnostic to Measure Emittance and Energy Spread Single shot electron beam measurements: charge, energy, energy spread, transverse emittance CCD magnetic spectrometer (1.2 T) ~1 m LBNL-LWFA Undulator ~ cm undulator radiation 0.5 GeV, Electron beam 2.18 cm period 66 periods K=1.25 plasma Laser beam e-beam grating Compact high-gradient quadrupoles ICT BPM BPM BPM phosphor imaged onto CCD Schematic layout: • Supporting systems: • Quads for refocusing • BPMs for positioning • OTR, phosphor screens

  5. Emittance and energy spread affect the undulator spectra

  6. Undulator radiation based diagnostic will allow for single shot DE/E and e measurement Changing energy spread / = 0.25% 1 mm-mrad / = 2.5% 1 mm-mrad Photons/shot/(0.1%BW) Photon energy (eV) Photons/shot/(0.1%BW) 6

  7. Experimental Setup in the Loasis lab Undulator Magnetic Spectrometer XUV Spectrometer

  8. THUNDER Undulator Magnetic Properties Magnetic Characteristics • Length = 1.5m • Magnetic period = 2.18cm • Number of periods = 66 • Peak Field = 0.61T • Wiggler Parameter K = 1.25 • Betatron period = 3.7m

  9. THUNDER tuned and characterized with the Spring-8 SPECTRA code Perfect B Field / = 0.25% 1 mm-mrad Real B Field / = 0.25% 1 mm-mrad Photons/shot/(0.1%BW) Photons/shot/(0.1%BW) E-beam trajectory before tuning E-beam trajectory after tuning Photon energy (eV)

  10. Quadrupoles transport E-beam to undulator

  11. New capillary chamber designed to fit quads and stages

  12. Micro-Channel Plate Based Spectrometer from 8 - 62nm Optical Characteristics XUV Spectrometer properties • First harmonic = 20nm • Natural divergence = 1 mrad • Pulse length = < 25 fs • First harmonic flux = 1x105 • 8-62nm spectral range • Four jaw Aperture System • MCP detector with CsI photocathode • Aberration corrected concave grating

  13. Characterization completed at the Advanced Light Source • Characterized on beamline 6.3.2 • 8-62nm Spectral Range • 0.07nm resolution at 20nm • Hitachi Aberration Corrected Concave Grating

  14. XUV Spectrometer Calibration Spectral Resolution vs. Wavelength Wavelength vs. Detector Position

  15. Conclusions and Future Work First experiments to begin this spring at Loasis • Undulator radiation can be used as a singe shot emittance and energy spread beam diagnostic • Experiments will be conducted using the Loasis LWFA at 500MeV • Undulator characterized and installed on beamline • XUV spectrometer built and characterized • Quadrupoles and magnetic spectrometer will be installed this spring This work is supported by the Defense Threat Reduction Agency and the Director, Office of Science, High Energy Physics, U.S. Dept. of Energy under Contract no. DE-AC02-05CH11231

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